Good luck finding the old hall, I remember heading up there as a kid through dense undergrowth and over barbed wire fences to get there, a very interesting place though. If you;re there on a guide trip it would be easier to get in but I don;t think it's open to the public.
As suggested above museum of Cannock Chase (which is in Hednesford) or the Marquis Drive VC where you can gen up on some local history and pick up the quaint map.
Freda's grave would be worthwhile stopping at if you;re walking past but the picture in the link you;ve posted is the extent of it.
The German war cemetery is a sombre place but interesting in a sobering way.
And then there's always Shugborough if you want a regular tourist attraction.